Reaction mechanism for the urea free phosphorylation of cellulose with phosphate esters in the presence of N, N-dimethyl acetamide

N,N-Dimethylacetamide (DMAc) was investigated as both a solvent and a catalyst for cellulose phosphorylation, as an alternative to urea. Herein, cellulose was phosphorylated using phosphate esters in the presence of either urea or DMAc to elucidate the differences between these two methods. The results demonstrated notable variations in the properties of the resulting celluloses. In the presence of urea, cellulose exhibited high phosphorus content (6.6%), a high total charge (3794 mmol/kg), and elevated water retention values, indicating strong hydrophilicity. In contrast, DMAc-treated cellulose displayed distinct properties, including a high water contact angle (108 °), low water retention values, and a low surface energy (26.73 mJ/m²), reflecting hydrophobic behavior. Thermogravimetric analysis confirmed that all phosphorylated celluloses maintained good thermal stability, even in the case of DMAc-treated cellulose with low phosphorus content (1.8%). Mechanistic insights were further obtained via GC-MS analysis, which revealed that phosphate esters initially react with DMAc to form dodecyl phosphoric acetic anhydride, subsequently reacting with cellulose to generate a network of flame-retardant and hydrophobic celluloses. These findings provide a foundation for understanding the role of DMAc in the phosphorylation process and for optimizing conditions for potential industrial applications. • Phosphorylated fibers are sustainable alternatives to fossil-based materials. • Their high hydrophilicity limits use in resin composites. • Replacing molten urea with DMAc increases phosphorus content and hydrophobicity. • Studying the phosphorylation mechanism with DMAc supports method scale-up. • The reaction occurs in two steps, releasing acetic acid.